Die blocks for thread rolling machines



Nov. 16, 1965 TEIJI sATo 3,217,530

DIE BLOCKS FOR THREAD ROLLING MACHINES Filed Jan. 2, 1963 3 Sheets-Sheet1 Tel]? Sofa INVENTOR BY LU 16 b Y m i ATTORNE TElJl SATO Nov. 16, 1965DIE BLOCKS FOR THREAD ROLLING MACHINES 5 Sheets-Sheet 2 Filed Jan. 2,1965 Nov. 16, 1965 TElJl SATO 3,217,530

DIE BLOCKS FOR THREAD ROLLING MACHINES Filed Jan. 2, 1963 3 Sheets-Sheet5 8 r" FIG" 1 Te/ji Sara INVENTOR BY whim ATTORNEY5 United States Patent3,217,530 DIE BLOCKS FOR THREAD ROLLENG MACHINES Teiji Sato, Sohka-shi,Saitama-ken, Japan, assignor to Katayama Rivet dz Screw Industrial (10.,Ltd, Tokyo, Japan, a company of Japan Filed Jan. 2, 1963, Ser. No.249,052 4 Claims. (Cl. 72-469) The present invention relates to a pairof matched die blocks which are movable relative to each other in athread rolling machine for rolling threads on self-tapping screws orWood screws. More particularly, the invention relates to theconfiguration of the working faces of said die blocks which enables thescrews which are rolled between the die blocks of a pair to be threaded,pointed and finished progressively during the course of a singlerelative movement of the blocks of a pair.

A comprehensive survey of the prior art by one familiar with threadrolling problems and the difficulties in making dies for rolling threadswould reveal prior patents evidencing the numerous efforts which havebeen made along various lines, to simultaneously thread and gimlet pointscrews. However, for reasons which are not important to the presentdiscussion, prior art dies have failed to live up to expectations andhave therefore not been endorsed by the art and have not come intowidespread adoption and use.

It is an object of the present invention to provide a pair of improveddie blocks which not only will roll and finish threads whilesimultaneously pointing self-tapping screws and wood screws, but whichwill also be possible to make economically by conventional manufacturingmethods and which will also be usable in conventional reciprocatingthread rolling machines.

Another object of the present invention is to provide a speciallydesigned working face on a screw threading die which is reliable andwhich will produce perfect screw threads without the difficulties whichare frequently encountered with conventional thread rolling dies, andwhich has accurately milled grooves which act on the shank of a screwblank with sufficient precision and certainty that the desired threadingand pointing action is satisfactorily carried out.

A still further object of the present invention is to provide die blockswhich will finish the threads and the points of the screws perfectly sothat no further manufacturing steps or operations need be performed onthem, and particularly which will produce screws having sharp pointedends which are free from burrs and which do not have the slight cavityor recess which is often present in the pointed ends of such screws.

It should be pointed out that during the development of die blocks ofthe present invention it was found that conventional thread rolling diescan be converted to dies according to the present invention by forming arecess in the die block and placing in said recess an insert having ashape according to the present invention to thereby convert theconventional die block into a die block according to the presentinvention.

It is to be understood that while for any particular pair of die blocks,the dimensions of the various parts of the surface are critical, theimportant feature of the invention generally is the shape andproportions of the surfaces of the die, and that by maintaining thesefactors and varying the dimensions, blocks can be made for rollingvarious sizes of screws.

Each die block of the pair of die blocks of the present invention is arectangular metal block having a flat back face, flat side faces,transverse end faces, as is common in such die blocks, and a workingface having a particular shape. The working face has a plurality ofobliquely extending thread forming groves and ribs, as is usual in suchthread forming die blocks, and in addition has a ridge gradually risingout of the working face of the die block beginning at a point spaced ashort distance from one end of the die block and extending obliquelytoward one edge of the die block and then substantially parallel to thesaid one edge, with the thread forming grooves and ribs extending up theface of the ridge facing the other edge of the die block.

A preferred embodiment of the invention will now be described in thefollowing specification with reference to the accompanying drawing, inwhich:

FIG. 1 is a perspective view of one die block of a pair of die blocksaccording to the present invention;

FIG. 2 is a plan view of two blocks of a pair of blocks according to thepresent invention at the starting position for rolling a headed screwblank between them;

FIGS. 3, 5, 7, 9, 11, 13 and 15 are schematic plan views similar to FIG.2 with the blocks in successive positions during their relative motionwhile threading, pointing and finishing a screw; and

FIGS. 4, 6, 8, 10, 12, 14 and 16 are sectional views taken alongrespective section lines 4--4, of FIG. 3, 66 of FIG. 5, 88 of FIG. 7,1010 of FIG. 9, 12-12 of FIG. 11, 14-14 of FIG. 13, and 16-16 of FIG.15.

As seen in FIG. 1 one of the die blocks of the pair of die blocksaccording to the present invention is a rectangular metal block having aflat back face 20, flat side faces 21 and 22, transverse end faces 23and 24, and a Working face 25. A large portion of the working face 25 isprovided with a plurality of uniformly spaced diagonal or obliquelyangled lengthwise extending grooves 26 and intervening ribs 27. Theseribs and grooves are gradually changed in width and depth from the end24 to the end 23, that is from the end at which the screw is initiallyacted on by the die block to the end at which the finished screw leavesthe die block, so as to start the threads gradually and gradually shapethem to the finished form desired.

Running along the block in the direction of its length starting from apoint spaced a short distance from the initially acting end 24; andtoward the finishing end 23 is a ridge 28 of gradually increasing heightwhich on the side toward the upper fiat face 21 has a profile 29gradually changing from a slight curve as shown in FIG. 6 to a morepronounced curve corresponding to the curvature of the pointed portionof the screw to be threaded, as seen in FIG. 10. The profile 3d of theside of the ridge 28 toward the lower flat side 22 drops off sharplyinto a recess 31 which runs along the lower portion of the working face25 from a point spaced a short distance from the initially acting end 24of the die block. The height of the pointed apex 32 of the ridge 28gradually increases until it approaches the finishing end of the block,see FIG. 14, at which point it stops rising and becomes substantiallylevel. As will be clear from a comparison of FIGS. 6 and 8, the ridge 28not only extends in the direction of the length of the die block in theportion where it starts to rise, but it also extends obliquely, alongone of the ribs 27, specifically along rib 27a, obliquely of the block.A first portion of recess 31 is cut back into the ribbed working face 25to the rib 27a at 31a, so that the side of the rib 27a forms the lowerprofile Ell of the ridge 27 at this point, and the apex 32 of the ridgeis formed by the top of the rib 27a. It will also be seen that the upperprofile of the ridge has ribs and grooves thereon, but these are ofreduced size, as seen in FIG. 8.

The oblique portion of the ridge 2? terminates in a first portion 28asubstantially midway of the length of the die block, and at this point asecond portion of the recess 31 is cut back into the working face 25 ofthe die block at 31b, the second portion of the recess cutting throughthe ridge 28 and being slightly deeper than recess 31a. This gives theillusion, as seen in FIG. 2, that the ridge drops abruptly, but inreality what is seen is a rib 27b, see FIG. 1, spaced several ribs awayfrom the ridge portion 28a, which rib is rising as it extends up theside of the ridge 2%. The edge of the second recess portion 31b alsoextends obliquely substantially parallel to the ribs 27, and as seen inFIG. 2, the ribs 27 along the edge are progressively higher until theyreach the peak of the ridge 28 at a second portion 28b near thefinishing end of the die block. From this point to the finishing end,the ridge 28 is of uniform height and extends substantially parallel tothe lower face 22 of the die block, as seen most clearly in FIG. 2, andas will be clear from the cross sections 14 and 16.

The other die block of each pair is identical to the die block describedabove, and when the pair of die blocks is placed in a machine for movingthe die blocks in opposite directions relative to each other, such as aconventional thread rolling machine, the two die blocks will haveinitial positions as shown in FIG. 2 with the initially acting ends 24opposed to each other. A headed screw blank S is placed between the dieblocks, and they are moved in opposite directions relative to eachother. This is usually accomplished by holding one of the die blocks,the lower block in FIGS. 2-16, in a fixed position and moving the upperblock along the lower block.

When the die blocks have been moved to the position shown in FIG. 3, thescrew blank has had the threads 33 started, but the overall shape of theshank of the screw is still substantially cylindrical, as seen in FIG.4, since the first part of the working face 25 is, with the exception ofthe grooves 26 and ribs 27, substantially flat. When the die blocks havebeen moved further to the position shown in FIG. 5, however, the shapeof the shank of the screw has started to change. At this point, theridges 28 on the working faces of the die blocks have started to riseout of the working faces 25, and since the blocks are a pair, these ribswill extend toward each other and squeeze the shank of the screw blank Sbetween them as shown in FIG. 6. Since the upper face 29 of each ridgecurves gradually upwardly, the profile of the screw shank will becorrespondingly rounded. It is also to be noted that the grooves 26 andthe ribs 27 have deepened the threads somewhat.

At this point on the working face of the die blocks, the ridges 28 arenot only rising out of the working face, but are angling obliquelydownwardly. As a result, when the blocks reach the positions shown inFIG. 7, the apexes 32 of the ridges 28 have not only pushed deeper intothe shank of the screw blank, but they have elongated the lower end ofthe blank by drawing it downwardly a distance d, as shown between FIGS.6 and 8. By this action, the pointed end of the screw is drawn and alsorolled to produce a hard pointed end without producing cracks or rollingover the ends of the blank to leave a slight cavity or recess in the endof the screw which is a common defect in rolled screws.

From this point to the position of the die blocks shown in FIG. 9, theridges 28 rise relatively little, and the point of the screw issharpened only slightly more than it was in the position of FIGS. 7 and8. Further, the grooves 26 and ribs 27 on the upwardly sloping side 29of the ridges 28 are less pronounced so that the threads on the shankare not very pronounced in the position as shown in FIG. 9.

As the die blocks are moved further, however, the screw is rolled overthe point at which the recesses 31b are cut back into the working faces25 of the die blocks, and as seen in FIGS. 11 and 12, the height of thedie face is reduced and the highest point of the die is farther awayfrom the lower edge of the blocks than the point just preceeding therecess 31b and the points farther along the block by a distance e, seeFIGS. 12 and 14. Thereafter, the working face of the block along theedge of the recess 31b rises and runs obliquely downwardly to the pointat which the ridge 28 is highest and where the opposed ap-exes 32 willapproach each other and cut the surplus material y from the pointed endof the screw and form a sharp point on the screw. Thereafter, as theblocks move through the position as shown in FIG. 15, the threads arefinished as seen in FIG. 16.

It will thus be seen that by the appropriate shaping of the workingfaces of the die blocks the screws which are threaded by being rolledbetween the blocks have accurately rolled threads and the points thereofare perfectly finished without cracks or recesses therein. Because ofthe simplicity of the method, screws can be mass produced with only asingle threading and finishing operation, and yet an excellent finishedscrew will be formed.

It is thought that the invention and its advantages will be understoodfrom the foregoing description and it is apparent that various changesmay be made in the form, construction and arrangement of the partswithout departing from th spirit and scope of the invention orsacrificing its material advantages, the form hereinbefore described andillustrated in the drawings being merely a preferred embodiment thereof.

What is claimed is:

1. A pair of die blocks for rolling screw threads in and pointing andfinishing a headed screw blank, each die block having a working facewith a plurality of obliquely extending thread forming grooves and ribs,and a ridge gradually rising out of the working face of said die blockbeginning at a point spaced a short distance in from one end of said dieblock and extending obliquely toward one edge of said die block and thensubstantially parallel to said one edge of said die block, said threadforming grooves and ribs extending up the face of the ridge facing theother edge of said die block, and said die block having a recess thereinextending back into the working face thereof from said edge beginning ata point spaced from said one end of said die block, the ungrooved faceof said ridge extending into said recess.

2. A pair of die blocks for rolling screw threads in and pointing andfinishing a headed screw blank, each die block having a working facewith a plurality of obliquely extending thread forming grooves and ribs,and a ridge gradually rising out of the working face of said die blockbeginning at a point spaced a short distance in from one end of said dieblock and extending obliquely toward one edge of said die block andsubstantially parallel to said grooves and ribs and then substantiallyparallel to said one edge of said die block, said thread forming groovesand ribs ex tending up the face of the ridge facing the other edge ofsaid die block, the said lastmentioned face of the ridge having aslightly curved profile in the lower part of said ridge and the profilegradually becoming more pronouncedly curved as the height of the ridgeapproaches a maximum, and said die block having a recess thereinextending back into the working face thereof from said one edgebeginning at a point spaced from said one end of said die block, theungrooved face of said ridge extending into said recess.

3. A pair of die blocks for rolling screw threads in and pointing andfinishing a headed screw blank, each die block having a working facewith a plurality of obliquely extending thread forming grooves and ribs,and ridge gradually rising out of the working face of said die blockbeginning at a point spaced a short distance in from one end of said dieblock and extending obliquely toward one edge of said die block andsubstantially parallel to said grooves and ribs and then substantiallyparallel to said one edge of said die block, said thread forming groovesand ribs extending up the face of the ridge facing the other edge ofsaid die block, the said lastmentioned face of the ridge having aslightly curved profile in the lower part of said ridge and the profilegradually becoming more pronouncedly curved as the height of the ridgeapproaches a maximum, said die block having a recess extending back intothe working face thereof from said one edge and said recess having afirst portion extending into the grooved and ribbed portion of theworking face at a point spaced a short distance from one end of the dieblock and having the edge of the recess running parallel to said ribsand grooves, the said ridge having the unribbed and ungrooved sidethereof falling sharply off into said first portion of said recess, andsaid recess having a second portion extending into the grooved andribbed portion of the Working face through said ridge at a point nearthe middle of said die block and having the edge of the recess runningparallel to said ribs and grooves, the rib extending along the edge ofsaid second portion of said recess falling sharply off into said secondportion of said recess.

4. A pair of die blocks as claimed in claim 3 in which the secondportion of the recess in each die block is deeper than the first portionof the recess.

References Cited by the Examiner UNITED STATES PATENTS Re. 5,673 12/1873Croft 80--8 15,512 8/1856 Gardner 80-9 440,333 11/1890 Rogers 808510,109 12/1893 Bement 808 FOREIGN PATENTS 435,690 3/1948 Italy.

CHARLES W. LANHAM, Primary Examiner.

MICHAEL V. BRINDISI, Examiner.

1. A PAIR OF DIE BLOCKS FOR ROLLING SCREW THREADS IN AND POINTING ANDFINISHING A HEADED SCREW BLANK, EACH DIE BLOCK HAVING A WORKING FACEWITH A PLURALITY OF OBLIQUELY EXTENDING THREAD FORMING GROOVES AND RIBS,AND A RIDGE GRADUALLY RISING OUT OF THE WORKING FACE OF SAID DIE BLOCKBEGINNING AT A POINT SPACED A SHORT DISTANCE IN FROM ONE END OF SAID DIEBLOCK AND EXTENDING OBLIQUELY TOWARD ONE EDGE OF SAID DIE BLOCK AND THENSUBSTANTIALLY PARALLEL TO SAID ONE EDGE OF SAID DIE BLOCK, SAID THREADFORMING GROOVES AND RIBS EXTENDING UP THE FACE OF THE RIDGE FACING THEOTHER EDGE OF SAID DIE BLOCK, AND SAID DIE BLOCK HAVING A RECESS THEREINEXTENDING BACK INTO THE WORKING FACE THEREOF FROM SAID EDGE BEGINNING ATA POINT SPACED FROM SAID ONE END OF SAID DIE BLOCK, THE UNGROOVED FACEOF SAID RIDGE EXTENDING INTO SAID RECESS.